1. Field of the Invention
The present invention relates to a self-expanding medical occlusion device for treating heart defects in patients, in particular closing abnormal openings in tissue, whereby the occlusion device is introduced into the body of a patient in minimally invasive fashion using a catheter system and consists of a braiding of thin threads, whereby the braiding exhibits a first preliminarily definable shape as the occlusion device is being inserted into the patient's body and a second preliminarily definable shape in the implanted state of the occlusion device, whereby the braiding of said occlusion device in the first profile form is in a collapsed state and the braiding in the second profile form is in expanded state.
2. Description of the Related Art
The principle behind this type of occlusion device is known to at least some extent in medical technology. For example, an occlusion device for treating septum defects is known from DE 10 338 702 of Aug. 22, 2003, consisting of a braiding of thin wires or threads and given a suitable profile in a molding and heat treatment process. The known occlusion device has a proximal retention area which is particularly distinctly flat, a distal retention area, and a cylindrical crosspiece between said proximal and distal retention areas. The ends of the wires forming the braiding converge into a holder in the distal retention area. This is hence designed as such so that the two retention areas of the known occlusion device will position on the two sides of a shunt to be occluded in a septum, usually by means of an intravascular surgical procedure, while the crosspiece will transverse the shunt.
Medical technology has long endeavored to be able to occlude septal defects, for instance atrioseptal defects, by means of non-surgical transvenous catheter procedures, in other words, without having to perform an operation in the literal sense. Various different occlusion systems have been proposed, each with their own pros and cons, without any one specific occlusion system having yet become widely accepted.
In making reference to these different systems, the following will use the terms “occluder” or “occlusion device.” In all interventional occlusion systems, a self-expanding umbrella system is introduced transvenously into a defect to be occluded in a septum. This type of system might comprise two umbrellas: one, for example, positioned at the distal side of the septum (i.e. the side furthest from the median plane of the body/heart) and one at the proximal side of the septum (i.e. the side closer to the median plane of the body), whereby the two umbrella prostheses are subsequently secured to a double umbrella in the septal defect. Thus, in the assembled state, the occlusion system usually consists of two clamped umbrellas connected to one another by means of a short bolt transversing the defect.
However, a disadvantage to such prior art occlusion devices turns out to be the relatively complicated, difficult and complex implantation procedure. Apart from the complicated implantation of the occlusion system in the septal defect to be occluded, the umbrellas utilized are susceptible to material fatigue along with fragment fracture. Furthermore, thromboembolic complications are frequently to be anticipated.
In order to enable the inventive occlusion device to be introduced by means of a surgical insertion instrument and/or guidewire, a holder is provided at the end of the distal retention area which can engage with the insertion instrument and/or guidewire. It is thereby intended that this engagement can be readily disengaged after positioning the occlusion device in the defect. For example, it is possible to devise the braiding at the end of the distal retention area of the occlusion device in such a manner so as to create an internal threading in the holder to engage with the insertion instrument. Of course, other embodiments are naturally also conceivable.
With another type of occlusion device, the so-called Lock-Clamshell umbrella system, two stainless steel preferably Dacron-covered umbrellas are provided, each stabilized by four arms. This type of occluder is implanted into the patient through a vein. However, seen as problematic with the Lock-Clamshell occluder is the fact that the insertion instruments necessary to implant the device need to be of relatively large size. A further disadvantage seen with other systems, for example the Amplatz occluder, is that many different occluder sizes are needed in order to cope with the respective dimensions of the septal defects to be occluded. It thus turns out that the umbrellas do not flatten out completely in the inserted state if the length or the diameter of the crosspiece inserted into the defect is not of an optimum match. This results in incomplete endothelialization. It has furthermore been shown that many of the systems implanted into patients' bodies exhibit material fatigue and fractures in the metallic structures due to the substantial mechanical stresses over a longer period. This is especially the case given permanent stress between an implant and the septum.
In order to overcome these disadvantages, self-centering occlusion devices have been developed which are inserted into the body of the patient and introduced into the septal defect to be occluded by way of a minimally invasive procedure, for example using a catheter and guidewires. Their design is based on the principle that the occlusion device can be tapered to the dimensions of the insertion instrument and/or catheter used for the intravascular procedure. Such a tapered occlusion device is then introduced by catheter into the septal defect to be occluded, respectively into the shunt of the septum defect to be occluded. The occluder is then discharged from the catheter, upon which the self-expanding umbrellas, retention plates respectively, subsequently unfold against the two sides of the septum. The umbrellas in turn comprise fabric inserts made from or covered by, for example, Dacron, with which the defect/shunt is occluded. The implants remaining in the body are more or less completely ingrown by the body's own tissue after a few weeks or months.
An example of a self-centering occlusion device of the type specified is known from WO 99/12478 A1, which is a further development of the occlusion device known as the “Amplatz occluder” in accordance with US printed U.S. Pat. No. 5,725,552. Same consists of a braiding of a plurality of fine, intertwined nitinol wire strands in the shape of a yo-yo. Each braiding is produced in its original form as a rounded braiding having loose wire ends both at its leading end (its proximal side, respectively) as well as at its trailing end (its distal side, respectively). During the subsequent processing of the rounded braiding, each of these loose ends must then be gathered into a sleeve and welded together. After the appropriate processing, both the proximal side as well as the distal side of the finished occluder exhibit a protruding collar. Dacron patches are sewn into the distal and proximal retention umbrellas and the interposed crosspiece. Because of the memory effect exhibited by the nitinol material used, the two retention umbrellas unfold by themselves upon exiting the catheter, initially in a balloon-like intermediate stage, whereby the retention umbrellas ultimately positioned on the two sides of the septum eventually assume a more or less flattened form. The crosspiece centers itself automatically into the shunt to be occluded during the positioning of the umbrellas.
The shape memory nitinol material known from prior art occlusion devices and that as previously described has, however, proven to have certain disadvantages with respect to occlusion devices. Nitinol, which is an atomistic alloy of nickel and titanium, is only conditionally suitable as a shape memory material for medical occlusion devices because the maximum deformation for nitinol between the first preliminarily definable shape given as the occlusion device is being inserted into the body of the patient and the second preliminarily definable shape given when the occlusion device is in implanted state only amounts to about 8%. In other words, this means that the shape memory nitinol material is only conditionally suitable for collapsing an occlusion device as small as possible for the implantation procedure. Hence, the implantation procedure when using a medical occlusion device which has braiding made from nitinol is not a particularly gentle one on the patient. Moreover, being an alloy of nickel and titanium, nitinol constitutes a permanent foreign body such that once in the implanted state, relevant defense system reactions can be expected from the body.
On the basis of the problematic task as set forth, which is in particular coupled with the use of nitinol as a shape memory material for medical occlusion devices, the task on which the present invention is based is that of improving upon a self-expanding medical occlusion device of the type specified at the outset to afford the patient a gentler implantation of the device.